SPC Aug 17, 2020 0600 UTC Day 1 Convective Outlook

SPC 1200Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0100 AM CDT Mon Aug 17 2020

Valid 171200Z - 181200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
CENTRAL AND EASTERN OREGON...

...SUMMARY...
Isolated severe storms capable of strong wind gusts are expected
this afternoon and evening from northern California, central and
eastern Oregon into far western Idaho. Other storms with strong
gusts are possible across parts of southern Arizona, south Texas
and a portion of the Middle Atlantic.

...Eastern Oregon and far western Idaho...

Plume of subtropical moisture is spreading northward through CA and
the Pacific NW within belt of stronger winds aloft along western
periphery of an upper ridge centered over the Great Basin. RAP
analysis and satellite data show a couple of vorticity maxima over
the eastern Pacific that will reach northern CA by mid afternoon and
continue through Oregon. This region will also reside within the
western fringe of steeper mid-level lapse rates and diabatic heating
of the boundary layer with dewpoints generally in the 40s to low 50s
F will support up to 500 J/kg MLCAPE. High based storms are expected
to develop within deeply mixed boundary layers over northern CA and
spread northeast through OR. Some CAMS suggest enough storms will
develop to establish a larger cold pool, possibly resulting in a
more widespread damaging wind threat from late afternoon into mid
evening. 

...Southern Arizona...

Pattern on Monday will change little from Sunday with northeasterly
winds aloft along southern periphery of an upper ridge centered over
the Great Basin. This pattern will once again favor storms that
develop over the higher terrain spreading southwestward into the
desert valleys where deep inverted-v profiles will support a threat
for isolated downburst winds.  

...Southern Texas...

A convective outflow is currently moving southward toward south TX,
and this boundary will probably stall and become the focus for
additional thunderstorm development later this afternoon. Moderate
instability and a destabilizing boundary layer will support a modest
threat for a few locally strong to damaging gusts with
multicell/pulse storms developing in a weak shear environment.

...Middle Atlantic region...

Upper trough will advance through the eastern states accompanied by
a cold front. A belt of stronger winds aloft will spread across
this region, but flow in the surface-500 mb layer is forecast to
remain relatively weak/modest. Corridor of modest instability with
500-1500 J/kg MLCAPE will likely develop east of the mountains,
where scattered storms are expected to initiate along the cold
front. A few locally strong wind gusts might accompany the stronger
storms, but the marginal thermodynamic environment with weak lapse
rates should serve as an overall limiting factor.

..Dial/Bentley.. 08/17/2020

Read more

from SPC Forecast Products http://www.spc.noaa.gov/products/outlook/day1otlk_1200.html